1. Field of the Invention
The subject invention generally pertains to industrial doors having a pliable door curtain, and more specifically to a system responsive to a door impact.
2. Description of Related Art
Industrial doors in which the door itself is made of pliable material such as fabric are used in a variety of applications, typically for the purpose of separating areas within a building, or closing off building doorways that lead outside. Examples of such pliable doors are planar doors, overhead-storing doors, concertina doors and roll-up doors. Planar doors include frame members on which the fabric comprising the door is disposed. This plane of material is then movable between a doorway blocking position and a storage position, wherein the plane of material and associated frame members are disposed above the doorway. The frame typically includes extensions extending past either side of the door, and which are receivable within guide tracks to guide the door through its vertical movement. These extensions may include wheels or trolleys. An overhead-storing door is similar in that the fabric door is maintained on frame members and is movable between doorway blocking and storage positions. In this door, however, the storage position is overhead, as in a typical garage door. Accordingly, the guide members associated with such a door will curve between the vertical and horizontal. A concertina door includes a fabric panel supported by spaced-apart ribs or stays that are guided for movement along a track. As the ribs travel along the track, the fabric panel folds and unfolds between the ribs to respectively open and close the door. A typical roll-up door comprises a roll-up panel or fabric curtain that is wound about a roller journalled for rotation above the doorway. To close the door, the roller pays out the curtain as two vertical tracks disposed along either side edge of the doorway guide the side edges of the curtain generally along a vertical plane across the doorway. The rotation of the roller is reversed to open the door. Roll-up doors are typically either powered open and closed, or are powered open and allowed to fall closed by gravity. As the invention herein is envisioned for use primarily with roll-up doors, it will be described it reference thereto. However, the invention may also be used in combination with other such pliable industrial doors.
Some roll-up doors have a rigid leading edge provided by a rigid or semi-rigid bar disposed along a lower portion of the curtain. The rigidity of the bar helps keep the curtain within the side tracks and helps the curtain resist wind and other air pressure differentials that may develop across opposite sides of the door.
Other roll-up doors, however, have a curtain with a relatively soft leading edge, To help keep such a curtain within its guide tracks, as well as keep the curtain taut and square to the doorway, opposite ends of the bottom portion of the curtain can be held in tension by two opposing carriages or trolleys that are constrained to travel along the tracks: one in each track. However, the door's lower leading edge does not necessarily have to be held in tension, especially when the door is not subject to significant pressure differentials.
Industrial doors are commonly installed in warehouses, where the doors are very susceptible to being struck by forklifts or other vehicles. To protect the door and the vehicle from damage and to protect personnel in the vicinity of the collision from injury, often some type of breakaway or compliant feature is added to the door. For a door having a rigid reinforcing bar along its leading edge, the bar may be provided with sufficient flexibility and resilience to safely pop out of its track when struck. Alternatively, a hard edge door may have its bottom bar connected at either end to carriages engageable with the tracks such that the bottom bar breaks away from the carriages for an impact. Doors having a relatively soft leading edge may have sufficient flexibility to absorb an impact, or a bottom portion of the door's curtain can be coupled to its two guide carriages by way of a breakaway coupling. The coupling releases the curtain from the carriage upon being subjected to a predetermined breakaway force, thereby limiting the impact force to a predetermined safe level. More information on breakaway couplings can be found in U.S. Pat. No. 5,638,883, which is specifically incorporated by reference herein.
A collision can also occur when a door accidentally closes upon an obstacle in its path, such as an object or a person. To protect the door and obstacle from damage or injury, often some type of switch is installed generally along the lower portion of the door to detect when an obstacle has been encountered. An example of such a switch would be an elongated bumper switch, tape-switch or some other elongated switch extending along the lower, leading edge of the roll-up panel. In reaction to sensing the obstacle upon impact, a set of electrical contacts of the switch typically close to stop or reverse the motor that drives the roller.
However, such switches are impractical for use on a door having a relatively soft leading edge, because the normal flexing of the door curtain could trip the switch prematurely. This can happen regardless of whether the soft leading edge of the curtain is held taut or left relatively loose. Therefore, some doors with a soft leading edge instead include a switch with normally closed contacts that are held open by the tension in the leading edge of the curtain. When an impact forces the leading edge of the curtain to break away from its guide tracks, the resulting release of tension within the curtain allows the switch's contacts to close. The closed contacts provide a signal that can be conveyed to the door's control circuit or an alarm circuit by way of a wire or battery powered radio transmission. Alternatively, a sensing mechanism may be associated with the guide carriages or trolleys associated with the soft edge. This sensing mechanism has a first state when the breakaway connection to the leading edge is intact, and a second state upon breakaway. This change to this second state is detected to stop or reverse the door.
In hard edged doors with a tape switch or other elongated switch, such elongated switches are typically inserted into a sheath attached to the curtain or incorporated within the curtain itself to allow a more durable or suitable sealing member to be installed just below the switch. This allows the very bottom or leading edge of the roll-up panel to be provided with a more compliant sealing material that can effectively conform to seal against the floor beneath the doorway when the door is closed. However, installing switches in such a manner, makes them rather inaccessible for servicing. Serviceability is particularly important, as the switch itself, being disposed along the lower portion of the roll-up panel, places the switch's electrical contacts and other electrical parts in a vulnerable position where they are subject to repeated impacts that could eventually damage the switch.
Further, when such a switch is used on a door having a breakaway coupling, wiring connecting the switch to a terminal associated with the motor's control needs to accommodate the separation of the coupling. That is often accomplished by running a separate coiled wire (i.e., multi-conductor cable) along the outside of the track and extending the wire from the terminal to the switch. Such a wire is usually coiled so it can stretch to accommodate the up and down motion of the door panel as well as the motion of the panel upon breaking away from its carriage. However, an exposed coiled wire can be unsightly, especially when it becomes permanently stretched out from use and begins to sag. As the wire sags, it becomes prone to snagging adjacent parts of the door or other items nearby.